Voltage regulators are commonly used for providing a regulated voltage and current starting from a supply voltage that may be variable over time. This allows properly supplying electronic circuits that require stable voltages and currents within well-defined, ideal ranges of values.
The most widespread type of regulator is the one called a charge pump. The charge pump regulators, or simply charge pumps, are formed by a plurality of cascade-connected elementary pumping stages (each of which provides an output voltage greater than an input voltage by a substantially constant value). Each charge pump may be implemented with components (e.g., transistors and/or capacitors) capable of withstanding high voltages—referred to as “High Voltage”, or HV components—or only low voltages—referred to as “Low Voltage”, or LV components. In the case in which HV components are used the charge pump will have better performance with high values of the supply voltage; such a charge pump, however, involves a considerable area occupation. On the contrary, the charge pump made with LV components will have better performance with reduced values of the supply voltage; such a charge pump, however, may require protection circuits against over-voltages.
In the art there is known to provide charge pumps having selectively connectable pumping stages to adapt the number of active pumping stages according to the desired value of the regulated voltage (e.g., as described in U.S. Pat. No. 6,927,441 and U.S. 2010/033232, whose entire disclosures are herein incorporated by reference). However, such techniques may require a very complex control circuit of selection switches, to manage the connections between the pumping stages.
A typical application of voltage regulators is in portable electronic systems without a local electric energy source (e.g., batteries) for reasons of available space. Examples of such electronic systems are so-called smartcards. The smartcards have a wide distribution in the banking, transport and recognition fields, where they are used for uniquely and securely accessing dedicated services. Such portable electronic systems derive the energy required for their operation from corresponding electronic devices (or readers) that use them.
Currently, there is a development of technologies for remote interactions between these portable electronic systems and the corresponding readers without physical contact (contact-less). In the contact-less technology the electric energy for operation of the portable electronic systems is provided via radio frequency (RF) signals—i.e., electromagnetic waves. In detail, the energy associated with the carrier of the RF signals sent by each reader (provided with a transceiver for exchanging data with each portable electronic system), is absorbed by an appropriate receiver circuit of the portable electronic system that transforms it into the supply voltage.
A problem of the portable electronic systems is that the energy absorbed through the RF signals a very variable intensity over time (depending mainly on distance and obstacles between the reader and each portable electronic system). Consequently, the power supply voltage provided by the receiver circuit (from the energy absorbed) will also be variable over time (e.g., the supply voltage may vary within a range of values from 1V to 5V).
However, without a voltage supply of adequate value, the charge pump of the portable electronic device may not be able to provide the regulated voltage and the regulated current with sufficient values to allow the proper operation of the electronic circuits connected thereto. In addition, very steep variations of the values of the supply voltage may prevent a complete charging of the capacitors used in the pumping stages. Consequently, the operation of the pumping stages may be compromised, which may cause a block situation of the charge pump (i.e., the regulated voltage and current are not provided with the desired values or they are not provided at all).
This variability of the regulated voltage and current may result in incorrect operation of the circuits that receive them. The above-mentioned problem may be particularly experienced in electronic circuits, such as memories of the EEPROM and FLASH type.